"Leading up to April 20, each of the companies had data and each was responsible for operations, and if data had been shared differently and operations had been carried out differently, I believe this disaster could have been prevented," said Richard Sears, an engineering expert who advised the panel.
"For a number of reasons, it didn't happen that way, and that's sad," he said as the panel wrapped up a two-day hearing into the accident on April 20, in which 11 workers died when an explosion rocked a BP-leased oil rig in the Gulf of Mexico.
Earlier Tuesday, a co-chair of the panel, William Reilly, said the three companies involved -- BP, oil services provider Halliburton and Transocean, which owned the rig -- were safety laggards in need of top-to-bottom reform.
Reilly blamed the rig explosion on a "culture of complacency" that ran through the three firms, and said all three had made a "suite of bad decisions" as they worked to drill a well more than a mile beneath the surface of the Gulf.
The seven-member panel set up by US President Barack Obama six months ago is tasked with trying to determine what caused the accident, which triggered a massive oil spill that is still impacting the Gulf environment and economy.
It is due to present its findings to Obama on January 11.
What the stars mean:
★ Poor ★ ★ Promising ★★★ Good ★★★★ Very good ★★★★★ Exceptional